In general, in a rear wheel drive or four-wheel drive four-wheel vehicle, motive power from a transmission device is transmitted to a final reduction gear device provided in the center of left and right rear wheels, via a propeller shaft which extends in a front/rear direction in the center of the vehicle width direction. Here, a critical speed of the propeller shaft needs to be set higher than a practical rotational speed range, and therefore the propeller shaft is divided into appropriate lengths.
For example, if the propeller shaft is divided into two pieces, then as shown in FIG. 8, the propeller shaft 200 is constituted by a first shaft 201 on the front side (one side), a second shaft 202 on the rear side (other side), and a constant-velocity joint 300 which couples the first shaft 201 and the second shaft 202. A front end portion of the first shaft 201 is connected to an output shaft (not illustrated) of the transmission device via a first universal joint 211 (cross joint, etc.), and a rear end portion of the second shaft 202 is connected to a drive pinion (not illustrated) of the final reduction gear device via a second universal joint 212.
As shown in FIG. 9, the constant-velocity joint 300 is a tripod type joint and is constituted by a bottomed round tubular outer ring 301 which is coupled to a rear end portion of the first shaft 201, a trunnion assembly 302 which slides in an axial direction inside the outer ring 301, and a shaft member 303, a front end portion of which is coupled to the trunnion assembly 302 and a rear end portion of which is coupled to a front end portion of the second shaft 202. A roller 304 of the trunnion assembly 302 slides or rolls along a sliding groove formed in an axial direction in an inner circumferential surface of the outer ring 301, whereby the outer ring 301 and the shaft member 303 extend and contract in the axial direction.
Here, the shaft member 303 is supported rotatably by a bearing 305 which is constituted by a ball bearing. The bearing 305 is prevented from detaching from the shaft member 303 by a stopper 306 having an L-shaped cross-section which is fixed to the shaft member 303.
The bearing 305 is fixed to a vehicle body (exterior) via an inner ring 307 (ring-shaped member), a mount 308 (ring-shaped elastic body, shock-absorbing rubber), an outer ring 309 and a bracket 310. The mount 308 is made of rubber and absorbs vibrations produced by imbalances in the propeller shaft 200 and vibrations produced by secondary couples of the universal joint.
Furthermore, a dust seal 311 and a dust seal 312 are provided at the front and rear of the bearing 305, so as to prevent the infiltration of water, dust or the like into the bearing 305. Lubricating grease for lubricating the bearing 305 is sealed in between the dust seal 311 and the dust seal 312.
Here, since the stopper 306 (shaft member 303) rotates and the inner ring 307 does not rotate, in front of the dust seal 311 (bearing 305), then the stopper 306 cannot abut against the inner ring 307 and hence the front side of the ring-shaped space formed between the stopper 306 and the inner ring 307 cannot be sealed off completely. Therefore, although it is considered that water, dust and the like, can readily infiltrate due to the provision of members which reduce the open portion of this space (the gap formed between the stopper 306 and the inner ring 307) as much as possible, since water which splashes up from the front wheels has a high pressure, there are cases where water and dust infiltrate through this gap. Therefore, technology of the following kind has been proposed.
In Japanese Examined Utility Model Application Publication No. S53-13147 and Japanese Patent Application Publication. No. 2008-208903, a lip (projection) is formed extending inward in a radial direction on a mount, and a front end of an inner radial side of the lip is made to contact a bearing member. In Japanese Unexamined Utility Model Application Publication No. S55-168428, a projection is formed in an integrated shape with a shock-absorbing rubber (mount), and the front end of the projection is inserted into a groove in a bearing member. In Japanese Patent Application Publication No. H7-101256, a front end of a steel inner ring is bent towards an inner radial side, thereby reducing the size of an opening portion. In Japanese Unexamined Utility Model Application Publication No. H1-119921, a lip extending outward in a radial direction is bonded by cure adhesion to a front end of an inner ring, and an outer radial end of the lip slides over a receiving member which rotates in unison with a shaft member, thereby preventing infiltration of water.
However, in the technology described in Japanese Examined Utility Model Application Publication No. S53-13147 and Japanese Patent Application Publication No. 2008-208903, since the lip and shaft member make contact, then there is a risk of abnormal noise occurring with the rotation of the shaft member. Furthermore, if the front end of the lip becomes worn, then a gap is formed between the lip and the shaft member, and there is a risk of water infiltrating through this gap. Moreover, since the lip is formed with a small thickness, then there is a risk of the lip deforming due to the water which splashes up from the front wheels, leading to infiltration of water.
Moreover, in the technology according to Japanese Unexamined Utility Model Application Publication No 555-168428, the groove in the shaft member becomes rusted due to the water, the depth and width of the groove decrease, and hence the gap between the groove and the projection becomes smaller, leading to a risk of abnormal noise.
Furthermore, in the technology according to Japanese Patent Application Publication No. H7-101256, since the inner ring and the rubber mount are bonded by cure adhesion, surface treatment of the inner ring is not possible. Therefore, rusting occurs on the exposed portions of the inner ring, and there is a risk of contact between the shaft member and portions of the inner ring that have expanded due to the rust.
Moreover, in Japanese Unexamined Utility Model Application Publication No. H1-119921, since the surface of the inner ring makes contact with the outside air, rusting occurs, and if this rust progresses to the interface between the lip and the inner ring, then the lip detaches from the inner ring, the gap becomes large, and there is a risk of infiltration of water.
In addition, in Japanese Examined Utility Model Application Publication No. S53-13147, Japanese Patent Application Publication No. 2008-208903, Japanese Unexamined Utility Model Application Publication No. S55-168428, Japanese Patent Application Publication No. H7-101256 and Japanese Unexamined Utility Model Application Publication No. H1-119921, when the vehicle travels through puddles, and so on, and the bearing is immersed in water, then water collects between the inner ring and the outer ring, and a problem arises in that this water cannot be readily discharged to the outside.
Therefore, it is an object of the present invention to provide a bearing structure in which the occurrence of abnormal noise and rusting is prevented, muddy water cannot readily infiltrate into one side of the bearing, and muddy water in the one side of the bearing is discharged to the outside in a satisfactory, manner.